Evaluation of gems, such as colored gems, often involves analysis of the spectral response of the gems to a variety of wavelengths of electromagnetic radiation, for example, in the UV, visible, and Near Infrared range, to search for indicators of color origin. Typical spectral responses can appear as a complex spectrum of peaks, slopes and plateaus over the wavelength range of interest.
For example, as described in the article, entitled “Insider Gemologist: Tests to Distinguish Natural from Treated Yellow Diamonds,” Feb. 23, 2001, Vol. 3, Issue 4, Gemological Institute of America, distinguishing natural-color yellow diamonds from treated ones may involve the use of a spectroscope to view the absorption spectra of a diamond for absorption bands known as the “Cape” lines, and for other lines. These Cape lines occur in most natural-color yellow diamonds at 478 nm, 465 nm, 452 nm. Other lines of interest may include a strong line at 415 nm. On the other hand, while treated diamonds may show one or more of these “Cape” lines, they also show a pair of strong absorption lines at 503 nm and 496 nm. In some cases an absorption band known as the “heat line” at 595 nm may be seen. The “heat line” is produced during an annealing step which transforms an irradiated diamond from a blue or green color to yellow. At the time of the article, the most common treatment for producing yellow color in diamonds was a combination of irradiation (either in a nuclear reactor or by use of an electron beam) and annealing, also known as controlled heating.
Conventional techniques for determining whether a gem stone has been subjected to color-altering treatment have involved the use of time consuming manual visual analysis of absorption spectra, or further evaluation of the results of generic spectral analysis algorithms, as well as the use of cumbersome cryostats, or other cooling techniques having their own disadvantages. As a result, such conventional analysis techniques suffer from significant per-stone analysis times. Further, the noise levels present in previous arrangements for acquiring spectral responses have limited the size of peaks that could be resolved in the acquired spectral responses. As a result of these and other limitations, conventional approaches typically rely on personnel who are highly skilled in spectral interpretation, have been prone to variations in consistency in applying analysis criteria to the acquired spectral responses, and have required substantial time to perform an analysis of each gem stone.
It is therefore desirable to have a method and system that is capable of the above spectral analysis in less time, with greater consistency, and with higher resolution than prior techniques.